Audio amplifier with embedded buck controller for class-G application

ABSTRACT

An audio amplifier includes: a buck controller configured to control an output voltage at a first supply terminal, the output voltage selected from a set including a plurality of output voltages, where the output voltage takes a settling time to settle; a first audio bridge including: a class-AB driver stage coupled to the first supply terminal, and a delay insertion circuit configured to receive a processed digital stream and provide the processed digital stream to the class-AB driver stage a delay time after receiving the processed digital stream, where the delay time is based on the settling time; and an audio amplitude detector configured to detect a first peak amplitude in the first digital audio stream, where the buck controller is configured to select a lowest output voltage from the set that is higher than the first peak amplitude plus a headroom voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/695,010, entitled “AUDIO AMPLIFIER WITH EMBEDDED BUCK CONTROLLER FORCLASS-G APPLICATION,” and filed on Nov. 25, 2019, which claims thebenefit of U.S. Provisional Application No. 62/771,967, entitled “AUDIOAMPLIFIER WITH EMBEDDED BUCK CONTROLLER FOR CLASS-G APPLICATION,” andfiled on Nov. 27, 2018, which applications are hereby incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates generally to an electronic system andmethod, and, in particular embodiments, to an audio amplifier withembedded buck controller for class-G application.

BACKGROUND

Power amplifiers are classified based on the characteristics of theoutput stage. In particular, the classes are based on the proportion ofeach input cycle in which the output device passes current. Conventionalclass-A amplifiers are simpler than class-B and class-AB amplifiers anduse a single amplifying transistor that is biased such that theamplifying transistor is always conducting. For differential class-Aamplifiers, the biasing point is typically selected to be equal to themaximum output current to allow for the amplification of the full rangeof the input signal.

Conventional class-B amplifiers use two amplifying transistors, eachoperating for half a cycle, in a push-pull configuration. Because of thenon-overlapping of the signals of each amplifying device, the class-Bamplifier typically has high crossover distortion.

Conventional class-AB amplifiers have a push-pull configuration thatoperates for more than half a cycle. To operate, class-AB amplifiers usebiasing circuits that are typically more complex than the biasingcircuits of class-A or class-B amplifiers. The overlap helps reduce thecross-over distortion present in class-B amplifiers at the expense ofhigher quiescent current.

FIG. 1 shows output stage 102 of conventional class-AB audio poweramplifier 100 for driving audio speaker 106. A controller and gatedrivers (not shown) control transistors 120, 122, 124 and 128 based onan audio input signal (which may be analog or digital).

A class-D amplifier is a switching amplifier that operates the outputtransistors as electronic switches instead of in the linear region. FIG.2 shows a schematic diagram of conventional class-D amplifier 200 fordriving audio speaker 106. Class-D amplifier includes comparator 202,drive circuit 204, output stage 205, inductor 210, and capacitor 212.

During normal operation, comparator 202 receives audio input signal 216and triangular waveform 218 (e.g., a sawtooth waveform) and generatespulse-width modulation (PWM) signal 220. PWM signal 220 is used tocontrol drive circuit 204, which in turn drives transistors 206 and 208of output stage 205 based on PWM signal 220. Output stage 205 producesoutput signal 222, which drives speaker 106 through low pass filter(LPF) 209.

PWM signal 220 has a frequency that is typically higher than 20 kHz,causing the switching frequency of output signal 222 to also be above 20kHz, which is above the human's audible range. LPF 209 generally filtersout the switching noise generated by output signal 222.

SUMMARY

In accordance with an embodiment, an audio amplifier includes: a firstsupply terminal; a second supply terminal; a buck controller having asupply input configured to receive a battery voltage, the buckcontroller configured to control an output voltage at the first supplyterminal, the output voltage being selected from a set including aplurality of output voltages, where the output voltage at the firstsupply terminal takes a settling time to settle when the buck controllerchanges the output voltage from a first voltage of the set to a secondvoltage of the set, the second voltage being higher than the firstvoltage; a first audio bridge having an input configured to receive afirst digital audio stream and an output configured to be coupled to afirst speaker, the first audio bridge including: a class-AB driver stagecoupled to the first supply terminal and configured to be coupled to thefirst speaker, a digital signal processing circuit coupled to the inputof the first audio bridge, and a delay insertion circuit configured toreceive a processed digital stream from the digital signal processingcircuit and configured to provide the processed digital stream to theclass-AB driver stage a delay time after receiving the processed digitalstream, where the delay time is based on the settling time; and an audioamplitude detector having an input coupled to the input of the firstaudio bridge and configured to detect a first peak amplitude in thefirst digital audio stream, where the buck controller is configured toselect a lowest output voltage from the set that is higher than thefirst peak amplitude plus a headroom voltage.

In accordance with an embodiment, an integrated circuit including: afirst supply terminal; a second supply terminal; a battery supplyterminal; a buck controller having a supply input coupled to the batterysupply terminal, the buck controller configured to control an outputvoltage at the first supply terminal, the output voltage being selectedfrom a set including a plurality of output voltages, where the outputvoltage at the first supply terminal takes a settling time to settlewhen the buck controller changes the output voltage from a first voltageof the set to a second voltage of the set, the second voltage beinghigher than the first voltage; a first audio bridge having an inputconfigured to receive a first digital audio stream and an outputconfigured to be coupled to a first speaker, the first audio bridgeincluding: a class-AB driver stage coupled to the first supply terminaland configured to be coupled to the first speaker, a digital signalprocessing circuit coupled to the input of the first audio bridge, and adelay insertion circuit configured to receive a processed digital streamfrom the digital signal processing circuit and configured to provide theprocessed digital stream to the class-AB driver stage a delay time afterreceiving the processed digital stream, where the delay time is based onthe settling time; and an audio amplitude detector having an inputcoupled to the input of the first audio bridge and configured to detecta first peak amplitude in the first digital audio stream, where the buckcontroller is configured to select a lowest output voltage from the setthat is higher than the first peak amplitude plus a headroom voltage.

In accordance with an embodiment, a method includes: receiving a firstdigital audio stream; detecting a first peak amplitude in the firstdigital audio stream; selecting an output voltage of a buck converter sothat the output voltage is a lowest output voltage from a set of buckoutput voltages that is higher than the first peak amplitude plus aheadroom voltage; converting the first digital audio stream into ananalog audio signal; and providing the analog audio signal to a speakerusing a class-AB driver stage a delay time after the output voltage ofthe buck converter settles, where the class-AB driver stage receivespower from the buck converter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows an output stage of conventional class-AB audio poweramplifier for driving an audio speaker, and a load current sensorcircuit for sensing a load current flowing through the audio speaker;

FIG. 2 shows a schematic diagram of a conventional class-D amplifier fordriving the audio speaker;

FIG. 3 shows a curves illustrating the power consumption Ptot of theinternal components of a conventional class-AB amplifier andcorresponding efficiency η, respectively, as a function of output powerPo;

FIG. 4 shows a digital input class-AB audio power amplifier with anembedded buck controller, operating in a class-G configuration,according to an embodiment of the present invention;

FIG. 5 shows a graph of an audio output (delivered to a speaker),respective buck converter setting code fed to the buck converter of FIG.4 , and corresponding output level of the buck converter of FIG. 4 ,according to an embodiment of the present invention;

FIG. 6 shows an audio signal and corresponding modulated supply VCC,where VCC is provided by the buck converter of FIG. 4 , according to anembodiment of the present invention;

FIG. 7 shows an audio signal (sinewave) and corresponding modulatedsupply VCC, where VCC is provided by the buck converter of FIG. 4 ,according to an embodiment of the present invention;

FIG. 8 shows a schematic diagram of an audio bridge, according to anembodiment of the present invention; and

FIG. 9 shows a curve illustrating the power consumption of the internalcomponents of a conventional class-AB amplifier, and a curveillustrating the power consumption of the internal components of aclass-AB amplifier with embedded buck converter operating in a class-Gconfiguration, according to the present invention.

Corresponding numerals and symbols in different figures generally referto corresponding parts unless otherwise indicated. The figures are drawnto clearly illustrate the relevant aspects of the preferred embodimentsand are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments disclosed are discussed indetail below. It should be appreciated, however, that the presentinvention provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The description below illustrates the various specific details toprovide an in-depth understanding of several example embodimentsaccording to the description. The embodiments may be obtained withoutone or more of the specific details, or with other methods, components,materials and the like. In other cases, known structures, materials oroperations are not shown or described in detail so as not to obscure thedifferent aspects of the embodiments. References to “an embodiment” inthis description indicate that a particular configuration, structure orfeature described in relation to the embodiment is included in at leastone embodiment. Consequently, phrases such as “in one embodiment” thatmay appear at different points of the present description do notnecessarily refer exactly to the same embodiment. Furthermore, specificformations, structures or features may be combined in any appropriatemanner in one or more embodiments.

Embodiments of the present invention will be described in a specificcontext, a digital audio amplifier with a plurality of outputs.Embodiments of the present invention may be used in other circuits, suchas audio amplifiers with a single output, as well as for amplifiers thatreproduce non-audio signals, for example.

In an embodiment of the present invention, a class-AB amplifier with anembedded buck converter is used in a class-G configuration to achievelower power consumption, e.g., during light loads. An audio amplitudedetector is used to monitor the amplitude of a digital audio streamdelivered to a bridge, where the bridge is coupled to a speaker. Thebuck converter, which provides power to the bridge, increases ordecreases the output voltage of the buck converter to the lowest voltagethat provides enough headroom for the bridge to drive the speakerwithout clamping or distortion. A delay is introduced in the audiosignal processing chain inside the bridge to allow enough settling timefor the buck converter to reach a desired output.

Conventional power audio amplifiers are typically implemented usingclass-D amplifiers instead of class-AB amplifiers to reduce the powerconsumption. Although class-D amplifiers may use more expensive externalcomponents and may have worst electromagnetic interference (EMI) profilethan class-AB amplifiers, class-D amplifiers are generally much moreefficient than class-AB amplifiers. For example, FIG. 3 shows curve 302and 304 illustrating the power consumption Ptot of the internalcomponents of a conventional class-AB amplifier and correspondingefficiency η, respectively, as a function of output power Po.

FIG. 4 shows digital input class-AB audio power amplifier 400 withembedded buck controller 408, operating in a class-G configuration,according to an embodiment of the present invention. As shown in FIG. 4, digital input class-AB audio power amplifier 400 has N channels thatreceive N digital audio inputs (Input₁, Input₂, . . . , Input_(i), . . ., Input_(N)) and drive N corresponding speakers (106 ₁, 106 ₂, . . . ,106 _(i), . . . , 106 _(N)) with respective outputs (OUTP, OUTM) ofrespective audio bridges (404 ₁, 404 ₂, . . . , 404 _(i), . . . , 404_(N)), where N is a positive integer greater or equal to 1. In someembodiments, digital input class-AB audio power amplifier 400 withembedded buck controller 408 and the N audio bridges 404, e.g., may beimplemented in integrated circuit 410 in a single package having, e.g.,and in a monolithic substrate.

As shown in FIG. 4 , buck converter 420 includes embedded buckcontroller 408, transistor 412, Schottky diode 414, and output capacitor418. Buck converter 420 receives power from power supply VBAT, which maybe a battery of a car or a cellphone, for example, and delivers supplyvoltage VCC to audio bridge(s) 404. In some embodiments, buck converter420 is capable of providing up to 40 A at 18 V supply level. In someembodiments, buck converter 420 may provide even higher power. Otherembodiments may have maximum power capabilities lower than 40 A at 18 V.

During normal operation, Buck converter 420 provides power to audiobridge(s) 404, e.g., via VCC terminal. Digital input class-AB audiopower amplifier 400 receives digital input(s) (Input₁ . . . Input_(N)),e.g., from an external circuit (e.g., controller, memory, bus, etc.) orfrom another circuit inside integrated circuit 410. The digital input(s)are provided to respective audio bridge(s) 404. Audio bridge(s) 404generate an output (audio) signal at their respective outputs (OUTP,OUTM) based on the respective digital input (Input_(i)).

Audio amplitude detector(s) 405 monitors the digital input of thecorresponding audio bridge 404 and predicts the output signal amplitudethe corresponding audio bridge would produce at the respective outputs(OUTP, OUTM). Audio amplitude detector 405 may be implemented, forexample, in the digital domain and may monitor the real-time inputdigital signal. Audio amplitude detector(s) 405 provide, e.g., the peakamplitude of the predicted output signal to supply level selector 406.

Supply level selector 406 receives the peak amplitude of the predictedoutput signal from the audio amplitude detector(s) 405 and selects anoutput voltage level for buck converter 420 (e.g., using buck_code)based on the received peak amplitude(s). For example, in someembodiments, the supply level selector 406 configures buck converter 420to have an output voltage that is the lowest voltage that is higher thanthe highest received peak amplitude (plus a headroom voltage).

FIG. 5 shows graph 500 of audio output curve 502 (delivered, e.g., to aspeaker by an audio bridge 404), respective buck_code setting code fedto buck converter 420, and corresponding output level of buck converter420, according to an embodiment of the present invention. For the sakeof simplicity, it is assumed that audio output curve 502 represents thehighest voltage peaks from all N channels of digital input class-ABaudio power amplifier 400.

As shown in FIG. 5 , the output of buck converter 420 is adjusted to thelowest voltage that provides enough headroom for the output signals(OUTP, OUTM) of the audio bridge 4040 to drive the corresponding speaker106, e.g., based on the predicted output signal amplitude or theamplitude of the digital audio stream delivered to the audio bridge 404.

For example, in some embodiments, buck converter 420 may have threedifferent output levels (e.g. 8 V for buck_code 00, 11 V for buck_code01, and VBAT for buck_code 11). When the output audio signal (curve 502)has a peak below the lowest level (e.g., 6 V) the buck_code 00,corresponding to 8 V output of buck converter 420, is selected. When theoutput audio signal has a peak above the lowest level (e.g., 6 V) butbelow the second to lowest level (e.g., 9 V) the buck_code 01,corresponding to 11 V output of the buck converter, is selected. Whenthe output audio signal has a peak above the lowest level (e.g., 6 V)and the second to lowest level (e.g., 9 V) the buck_code 11,corresponding to VBAT output of buck converter 420, is selected.

In this embodiment, a 2 V headroom voltage is assumed. For example, an 8V VCC is used when the peak voltage is lower than 6 V). In someembodiments, a different headroom voltage, such as smaller than 2 V orhigher than 2V, may be used.

Other output levels for buck converter 420 may be used. As anothernon-limiting example, some embodiments may use 6 V, 9 V and VBAT as theoutput levels corresponding to buck_codes 00, 01, and 11, respectively.Other output levels may be used.

Some embodiments may have only two output levels for the buck converter.Other embodiments may have more than three possible output levels forthe buck converter.

Some embodiments may implement the output voltage selection using adigital-to-analog converter (DAC). Other implementations are alsopossible.

In some embodiments, all of the N channels of digital input class-ABaudio power amplifier 400 are monitored, and the output of buckconverter 420 is set to the lowest level that provides enough headroomto all of the N channels. For example, in an embodiment, if channel onehas a peak amplitude of 11 V but the other N−1 channels have a peakamplitude of less than 6 V, the VBAT setting is selected for buckconverter 420.

FIG. 6 shows audio signal 602 (from outputs OUTP, OUTM of an audiobridge 404) and corresponding modulated supply VCC (curve 604), whereVCC is provided by buck converter 420, according to an embodiment of thepresent invention. As shown in FIG. 6 , the supply VCC (curve 604) goeslow when the audio signal (curves 602) go low, and goes high when theaudio signal goes high, thereby advantageously allowing enough headroomto avoid clamping or otherwise distorting the audio signal while keepingthe VCC voltage low.

FIG. 7 shows audio signal 702 (sinewave) and corresponding modulatedsupply VCC (curve 604), where VCC is provided by buck converter 420,according to an embodiment of the present invention.

As shown in FIGS. 4-7 , buck converter 420 adjusts the buck outputvoltage VCC based on the digital audio inputs (Input₁ . . . Input_(N)).When it is determined that the buck output voltage VCC of buck converter420 should rise, the buck output voltage VCC should rise before theaudio output signal is delivered to the speaker 106. Some embodiments,therefore, insert a delay in the signal processing path of each audiobridge to allow the buck output voltage VCC to settle before the audiooutput reaches the speaker. For example, FIG. 8 shows a schematicdiagram of audio bridge 800, according to an embodiment of the presentinvention. Audio bridge 800 is a possible implementation of audio bridge404.

As shown in FIG. 8 the Digital Input (e.g., any of Input₁ . . .Input_(N)) is processed by digital signal processing circuit 802. Adelay is then inserted by delay insertion circuit 804 (e.g., in thedigital domain). A DAC is then used together with a class-AB driver(such as shown in FIG. 1 ) to drive the corresponding speaker 106. Insome embodiments, the delay inserted by the delay insertion circuit 804is determined based on the settling time of buck converter 420. Sinceall of the digital inputs are experiencing the same delay, no audiointerruptions or distortion is experienced by a listener.

In some embodiments, the settling time of buck converter 420 isdetermined as the time from change in the output voltage (e.g., changein buck_code) until voltage VCC is within, e.g., 5% of the target outputvoltage. Other tolerances, such as 7% or higher, or 2% or lower, mayalso be used. In some embodiment, the settling time may be differentdepending on the start buck_code and the end buck_code. In suchembodiments, the settling time used by delay insertion circuit 804 maybe the longest settling time of the possible settling times of the buckconverter 420. In some embodiments, the settling time used by delayinsertion circuit 804 may be longer than the longest settling time ofthe possible settling times of the buck converter 420.

Advantages of some embodiments include a reduction in power consumptionwhen compared to conventional class-AB implementations. For example,FIG. 9 shows curve 904 illustrating the power consumption of theinternal components of a conventional class-AB amplifier, and curve 902illustrating the power consumption of the internal components of aclass-AB amplifier with embedded buck converter operating in a class-Gconfiguration, according to the present invention. As shown, theclass-AB amplifier with embedded buck converter operating in a class-Gconfiguration (e.g., such as digital input class-AB audio poweramplifier 400 with embedded buck controller 408) consumes significantlyless power than a conventional class-AB amplifier during light loads. Insome embodiments, the dissipated power under average listeningconditions may be reduced up to 50% when compared to conventionalclass-AB amplifiers.

Buck converter 420 may be implemented in various ways. For example, insome embodiments buck (step-down) converter 420 generates a regulatedvoltage VCC by driving the control terminal of transistor 412 (atterminal GD) with a pulse-width modulation (PWM) signal that is based onthe feedback voltage (at terminal FB). The feedback voltage may bedivided using a voltage divider (not shown) and then compared with areference voltage (not shown) to generate the PWM signal. In someembodiments, the code buck_code changes the voltage divider to adjustthe output voltage generated by converter 420 at terminal VCC. Otherimplementations are also possible.

In some embodiments, a transistor may be used instead of Schottky diode414. In some embodiments, current may be sensed directly in an outputtransistor (e.g., transistor 412 and/or a low-side transistor replacingSchottky diode 414) and sense resistor 419 may be omitted. Otherimplementations are also possible.

Supply level selector 406 may include a digital comparator that comparesthe digital representation of the maximum voltage peak received from theN audio amplitude detectors 405, e.g., in a predetermined window oftime, and selects, e.g., based on a look-up table (LUT) storing the setof possible buck_codes, the buck_code that corresponds to the lowest VCCvoltage that has enough headroom for the maximum voltage peak received.Other implementations are also possible.

Audio amplitude detector(s) 405 may be implemented, e.g., using digitallogic, including registers, to store and/or send to supply levelselector 406 the digital representation of the maximum peak voltagedetected from the respective input, e.g., in a predetermined window oftime. Other implementations are also possible.

Speaker 106 may be implemented in any way known in the art. For example,in some embodiments, speaker 106 may have a 4Ω impedance. Otherimplementations are also possible.

Digital signal processing circuit 802 may be implemented as a custom orgeneral purpose processor, digital signal processor (DSP) or controller.Other implementations are also possible.

Delay insertion circuit 804 may be implemented, e.g., by gating a clockused to send information from digital signal processing circuit 802 toDAC and class-AB driver stage 806. Other implementations are alsopossible.

Although FIG. 8 shows that each audio bridge 800 includes a digitalsignal processing circuit 802 and a delay insertion circuit 804, is itunderstood that, in some embodiments, a centralized controller,processor or DSP may implement all of digital signal processing circuits802 and/or all of delay insertion circuits 804.

In some embodiments, the delay for processing the digital input bydigital signal processing circuit 802 may be longer than the settlingtime of buck converter 420. In such embodiments, delay insertion circuit804 may be optional.

DAC and class-AB driver stage 806 may be implemented with a conventionalDAC (e.g., using R2R ladder, delta-sigma modulation, or other), and aconventional class-AB driver stage, such as using a controller tocontrol a full-bridge, such as full-bridge 102.

Example embodiments of the present invention are summarized here. Otherembodiments can also be understood from the entirety of thespecification and the claims filed herein.

Example 1. An audio amplifier including: a first supply terminal; asecond supply terminal; a buck controller having a supply inputconfigured to receive a battery voltage, the buck controller configuredto control an output voltage at the first supply terminal, the outputvoltage being selected from a set including a plurality of outputvoltages, where the output voltage at the first supply terminal takes asettling time to settle when the buck controller changes the outputvoltage from a first voltage of the set to a second voltage of the set,the second voltage being higher than the first voltage; a first audiobridge having an input configured to receive a first digital audiostream and an output configured to be coupled to a first speaker, thefirst audio bridge including: a class-AB driver stage coupled to thefirst supply terminal and configured to be coupled to the first speaker,a digital signal processing circuit coupled to the input of the firstaudio bridge, and a delay insertion circuit configured to receive aprocessed digital stream from the digital signal processing circuit andconfigured to provide the processed digital stream to the class-ABdriver stage a delay time after receiving the processed digital stream,where the delay time is based on the settling time; and an audioamplitude detector having an input coupled to the input of the firstaudio bridge and configured to detect a first peak amplitude in thefirst digital audio stream, where the buck controller is configured toselect a lowest output voltage from the set that is higher than thefirst peak amplitude plus a headroom voltage.

Example 2. The audio amplifier of example 1, where the headroom voltageis 2 V or lower.

Example 3. The audio amplifier of one of examples 1 or 2, where the setincludes three output voltages.

Example 4. The audio amplifier of one of examples 1 to 3, where anoutput voltage of the set is the battery voltage.

Example 5. The audio amplifier of one of examples 1 to 4, where thesecond supply terminal is coupled to ground.

Example 6. The audio amplifier of one of examples 1 to 5, furtherincluding: a high-side transistor coupled between the supply input ofthe buck controller and an intermediate node; a diode coupled betweenthe second supply terminal and the intermediate node; and an inductorcoupled between the intermediate node and the input of the first audiobridge.

Example 7. The audio amplifier of one of examples 1 to 6, where the buckcontroller, the first audio bridge are integrated in an integratedcircuit, and where the high-side transistor, the diode, and the inductorare external to the integrated circuit.

Example 8. The audio amplifier of one of examples 1 to 7, furtherincluding a low-side transistor that includes the diode.

Example 9. The audio amplifier of one of examples 1 to 8, where thediode is a Schottky diode.

Example 10. The audio amplifier of one of examples 1 to 9, furtherincluding: a second audio bridge having an input configured to receive asecond digital audio stream and an output configured to be coupled to asecond speaker, the second audio bridge including: a second class-ABdriver stage coupled to the first supply terminal and configured to becoupled to the second speaker, a second digital signal processingcircuit coupled to the input of the second audio bridge, and a seconddelay insertion circuit configured to receive a second processed digitalstream from the digital signal processing circuit and configured toprovide the second processed digital stream to the class-AB driver stagea second delay time after receiving the processed digital stream, wherethe second delay time based on the settling time; and a second audioamplitude detector having an input coupled to the input of the secondaudio bridge and configured to detect a second peak amplitude in thesecond digital audio stream, where the buck controller is configured toselect a lowest output voltage from the set that is higher than thefirst peak amplitude plus the headroom voltage and is higher than thesecond peak amplitude plus the headroom voltage.

Example 11. The audio amplifier of one of examples 1 to 10, where thedelay time is higher than or equal to the settling time.

Example 12. An integrated circuit including: a first supply terminal; asecond supply terminal; a battery supply terminal; a buck controllerhaving a supply input coupled to the battery supply terminal, the buckcontroller configured to control an output voltage at the first supplyterminal, the output voltage being selected from a set including aplurality of output voltages, where the output voltage at the firstsupply terminal takes a settling time to settle when the buck controllerchanges the output voltage from a first voltage of the set to a secondvoltage of the set, the second voltage being higher than the firstvoltage; a first audio bridge having an input configured to receive afirst digital audio stream and an output configured to be coupled to afirst speaker, the first audio bridge including: a class-AB driver stagecoupled to the first supply terminal and configured to be coupled to thefirst speaker, a digital signal processing circuit coupled to the inputof the first audio bridge, and a delay insertion circuit configured toreceive a processed digital stream from the digital signal processingcircuit and configured to provide the processed digital stream to theclass-AB driver stage a delay time after receiving the processed digitalstream, where the delay time is based on the settling time; and an audioamplitude detector having an input coupled to the input of the firstaudio bridge and configured to detect a first peak amplitude in thefirst digital audio stream, where the buck controller is configured toselect a lowest output voltage from the set that is higher than thefirst peak amplitude plus a headroom voltage.

Example 13. The integrated circuit of example 12, further including: asecond audio bridge having an input configured to receive a seconddigital audio stream and an output configured to be coupled to a secondspeaker, the second audio bridge including: a second class-AB driverstage coupled to the first supply terminal and configured to be coupledto the second speaker, a second digital signal processing circuitcoupled to the input of the second audio bridge, and a second delayinsertion circuit configured to receive a second processed digitalstream from the digital signal processing circuit and configured toprovide the second processed digital stream to the class-AB driver stagea second delay time after receiving the processed digital stream, wherethe second delay time is equal to the delay time; and a second audioamplitude detector having an input coupled to the input of the secondaudio bridge and configured to detect a second peak amplitude in thesecond digital audio stream, where the buck controller is configured toselect a lowest output voltage from the set that is higher than thefirst peak amplitude plus the headroom voltage and is higher than thesecond peak amplitude plus the headroom voltage.

Example 14. A method including: receiving a first digital audio stream;detecting a first peak amplitude in the first digital audio stream;selecting an output voltage of a buck converter so that the outputvoltage is a lowest output voltage from a set of buck output voltagesthat is higher than the first peak amplitude plus a headroom voltage;converting the first digital audio stream into an analog audio signal;and providing the analog audio signal to a speaker using a class-ABdriver stage a delay time after the output voltage of the buck convertersettles, where the class-AB driver stage receives power from the buckconverter.

Example 15. The method of example 14, where the set includes three buckoutput voltages.

Example 16. The method of one of examples 14 or 15, where a first outputvoltage of the set is equal to a battery voltage received by the buckconverter.

Example 17. The method of one of examples 14 to 16, where the headroomvoltage is 2 V or lower.

Example 18. The method of one of examples 14 to 17, further including:receiving a second digital audio stream; detecting a second peakamplitude in the second digital audio stream; and selecting an outputvoltage of the buck converter so that the output voltage is a lowestoutput voltage from the set that is higher than the first peak amplitudeplus the headroom voltage and higher than the second peak amplitude plusthe headroom voltage.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method comprising: detecting a first peakamplitude in a first digital audio stream; selecting an output voltageof a converter such that the output voltage is a lowest output voltagefrom a set of output voltages, the set of output voltages comprising aplurality of voltage output values and each having a value higher thanthe first peak amplitude plus a headroom voltage; converting the firstdigital audio stream into an analog audio signal; and providing theanalog audio signal to a speaker using a class-AB driver stage with adelay time after the output voltage of the converter settles, whereinthe class-AB driver stage receives power from the converter.
 2. Themethod of claim 1, wherein the set comprises three output voltages. 3.The method of claim 2, wherein a first output voltage of the set issubstantially equal to a battery voltage received by the converter. 4.The method of claim 1, wherein the headroom voltage is 2 V or lower. 5.The method of claim 1, further comprising: receiving a second digitalaudio stream; and detecting a second peak amplitude in the seconddigital audio stream, wherein selecting the output voltage of theconverter comprises selecting the output voltage of the converter sothat the output voltage is the lowest output voltage from the set thatis higher than the first peak amplitude plus the headroom voltage andthat is higher than the second peak amplitude plus the headroom voltage.6. The method of claim 1, wherein selecting the output voltage of theconverter comprises selecting the output voltage from the set using a2-bit code.
 7. The method of claim 1, wherein selecting the outputvoltage comprises selecting the output voltage based on a look-up table(LUT) storing the set.
 8. The method of claim 1, wherein the converteris a buck converter.
 9. The method of claim 1, further comprisingdetermining the delay time based on a settling time of the outputvoltage.
 10. The method of claim 1, further comprising inserting thedelay time before converting the first digital audio stream into theanalog audio signal to provide the analog audio signal to the speakerthe delay time after the output voltage of the converter settles. 11.The method of claim 10, wherein inserting the delay time comprisesgating a clock.
 12. The method of claim 1, wherein the class-AB driverstage receives power from the converter via an inductor.
 13. The methodof claim 12, wherein the inductor is coupled between a current path of ahigh-side transistor and a capacitor.
 14. The method of claim 1, furthercomprising receiving a battery voltage from a battery, wherein a highestvoltage of the set is the battery voltage.
 15. The method of claim 1,wherein the set comprises 6 V and 9 V.
 16. The method of claim 5,further comprising: converting the second digital audio stream into asecond analog audio signal; providing the second analog audio signal toa second speaker using a second class-AB driver stage that receivespower from the converter; and causing the second analog audio signal tobe delayed by the delay time.
 17. A method comprising: detecting a firstpeak amplitude in a first digital audio stream; selecting an outputvoltage of a converter such that the output voltage is a lowest outputvoltage from a set of output voltages, the set of output voltagescomprising a plurality of voltage output values and each having a valuehigher than the first peak amplitude plus a headroom voltage; convertingthe first digital audio stream into an analog audio signal; andproviding the analog audio signal to a speaker using a class-AB driverstage with a delay time after the output voltage of the convertersettles, wherein the class-AB driver stage receives power from theconverter, wherein the set comprises three output voltages, and whereina highest voltage of the set is a battery voltage.
 18. The method ofclaim 17, wherein the set comprises 6 V and 9 V.
 19. A methodcomprising: detecting a first peak amplitude in a first digital audiostream; selecting an output voltage of a converter such that the outputvoltage is a lowest output voltage from a set of output voltages, theset of output voltages comprising a plurality of voltage output valuesand each having a value higher than the first peak amplitude plus aheadroom voltage; converting the first digital audio stream into ananalog audio signal; providing the analog audio signal to a speakerusing a class-AB driver stage with a delay time after the output voltageof the converter settles, wherein the class-AB driver stage receivespower from the converter; converting a second digital audio stream intoa second analog audio signal; providing the second analog audio signalto a second speaker using a second class-AB driver stage that receivespower from the converter; and causing the second analog audio signal tobe delayed by the delay time.
 20. The method of claim 19, wherein theclass-AB driver stage and the second class-AB driver stage receive powerfrom the converter via an inductor.